As semiconductor technology develops, the sizes of wafers are constantly increasing. The wafers with larger diameters make it possible to produce more semiconductor devices from a single wafer, and thus productivity and economic efficiency are significantly enhanced. In semiconductor manufacturing, various wet processes are performed on the wafers to remove portions of deposited material layers for patterning or to remove contaminants and particles on the wafers for cleaning. As the sizes of the wafers are continuously increased, batch type wet processing tools are gradually replaced by single wafer wet processing tools because the batch type wet processing tools for the large wafers become cumbersome, and the single wafer wet processing tools can offer better process control, lower cost and shorter cycle time.
However, while conventional single wafer wet processing tools have been generally adequate for their intended purposes, they have not been entirely satisfactory in every aspect.